Custom Controls can be created in the Device control section of Global Settings (see 2nd screen shot below). This can be used to play a sound, play a video or control devices connected by a Phidget relay such as lights, fans, etc. You could add multiple sound effects or videos and play those randomly from your phone.

To set up go to Global Settings and select Automation and Device Control (figure 1 below). Next, select Add Input and choose Booth Control Custom Input (figure 2 below). Add the name to display in the Custom Control screen (figure 3 below) and then use the normal add device setup to add any video, sound or Phidget control.